Publication Summary

Previous sampling of the Colville River has found bacteria violations of the state water quality standards during the summer months. In response to these impairments, the Washington State Department of Ecology conducted a total maximum daily load study for fecal coliform in the Colville River basin from March 2000 through March 2001. A total of 10 mainstem and 15 tributary and headwater sites were sampled every other week. Discharge during the study averaged 27% above normal. Study results showed violations of the state bacteria standards were widespread through the dry season.

Previous sampling of the Colville River has found bacteria violations of the state water quality standards during the summer months. In response to these impairments, the Washington State Department of Ecology conducted a total maximum daily load study for fecal coliform in the Colville River basin from March 2000 through March 2001. A total of 10 mainstem and 15 tributary and headwater sites were sampled every other week. Discharge during the study averaged 27% above normal.

Study results showed violations of the state bacteria standards were widespread through the dry season. Only the Sheep Creek site in Springdale, a headwater stream flowing from the uplands, and the most downstream site, the Colville River at Greenwood Loop Road, were without bacteria violations. The critical period for loading was between June and September, with the exception of Blue Creek. Blue Creek, a small tributary discharging to the Colville River at river mile 37, had the highest bacteria counts for the study. Work is underway to connect the community of Bluecreek to the newly constructed wastewater treatment facility in Addy in late 2002.

To determine reduction targets needed for compliance with water quality standards, rolling geometric means and 90th percentiles for bacteria counts were calculated for two- and three-month periods. The "statistical theory of rollback" was applied to determine the percentage of reduction in bacteria loads that would be needed during the critical period per river segment to bring water quality within standards. The percentage of load reductions needed per sub-basin ranged from 3% to 95%.

Link to EIM data for User Study ID RCOO0002